Abstract Plant root-derived labile carbon (C) delivered to soils can regulate the dynamics and turnover of soil organic matter (SOM); however, it remains largely unclear how inputs of individual labile components (e.g., glucose) affect the formation of physicochemical-protected SOM. In a firmly controlled rhizosphere system, we added a glucose solution through artificial roots to soils collected from two subalpine coniferous forests (an approximately 200-year-old spruce-fir forest and an approximately 70-year-old spruce plantation) with the soils subsequently incubated over 25 days. The results showed that the addition of glucose significantly increased the concentrations of aluminum (Al) and iron (Fe) bound in both metal-organic complexes (MOCs) and short-range order phases (SROs) by 45%, 68%, 31% and 38%, respectively (soil-averaged), which indicated that glucose addition enhanced the formation of physicochemical-protected SOM. The induced protection of SOM mainly resulted from the stimulation of interactions of the microbial residues with soil minerals and/or metal cations, as indicated by the concurrently increased microbial communities and zeta potential after glucose addition. Moreover, the glucose-induced absolute changes in MOCs at the spruce-fir site were higher than those at the spruce plantation site, whereas the changes in SROs exhibited an opposite trend to that observed for MOCs. This discrepancy is presumably due to the higher organic matter content with more extractable metals at the spruce-fir site being more beneficial for supporting microbial stabilization of glucose and subsequent necromass sequestration as MOCs. In addition, more clay minerals at the spruce plantation site had larger surface areas and more binding sites to bind microbial-derived organic molecules as SROs. Collectively, our findings provide robust evidence that the input of labile C to soils could facilitate the formation of physicochemical-protected SOM, which is potentially involved in transformation into microbial residues and subsequent interaction with metal cations and/or minerals and may also be mediated by soil properties. The formation of protected SOM may potentially offset native SOM decomposition and thus has ecologically important implications for long-term terrestrial C storage.

中文翻译：

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通过人工根系输入不稳定的 C 促进受保护 SOM 的形成

摘要 植物根系不稳定碳（C）输送到土壤中可以调节土壤有机质（SOM）的动态和周转；然而，在很大程度上仍不清楚单个不稳定成分（例如，葡萄糖）的输入如何影响物理化学保护的 SOM 的形成。在一个严格控制的根际系统中，我们通过人工根将葡萄糖溶液添加到从两个亚高山针叶林（一个大约 200 年历史的云杉冷杉林和一个大约 70 岁的云杉种植园）收集的土壤中，随后土壤培养超过 25 天。结果表明，葡萄糖的加入使金属有机配合物 (MOC) 和短程有序相 (SRO) 中结合的铝 (Al) 和铁 (Fe) 的浓度显着增加了 45%、68%、31%和 38%，分别（土壤平均），这表明葡萄糖的添加增强了物理化学保护的 SOM 的形成。SOM 的诱导保护主要是由于微生物残留物与土壤矿物质和/或金属阳离子的相互作用的刺激，如添加葡萄糖后微生物群落和 zeta 电位同时增加所表明的。此外，葡萄糖诱导的云杉-冷杉场地 MOCs 绝对变化高于云杉种植场地，而 SROs 的变化与观察到的 MOCs 趋势相反。这种差异可能是由于云杉-冷杉位点的有机物含量更高，可提取的金属更多，更有利于支持微生物稳定葡萄糖和随后作为 MOC 的死灵封存。此外，云杉种植园更多的粘土矿物具有更大的表面积和更多的结合位点，以结合微生物衍生的有机分子作为 SRO。总的来说，我们的研究结果提供了强有力的证据，表明向土壤中输入不稳定的 C 可以促进物理化学保护的 SOM 的形成，这可能涉及转化为微生物残留物以及随后与金属阳离子和/或矿物质的相互作用，也可能是由土壤特性。受保护的 SOM 的形成可能会抵消原生 SOM 的分解，因此对长期陆地碳储存具有重要的生态意义。我们的研究结果提供了强有力的证据，表明向土壤中输入不稳定的 C 可以促进物理化学保护的 SOM 的形成，这可能涉及转化为微生物残留物以及随后与金属阳离子和/或矿物质的相互作用，也可能由土壤性质介导. 受保护的 SOM 的形成可能会抵消原生 SOM 的分解，因此对长期陆地碳储存具有重要的生态意义。我们的研究结果提供了强有力的证据，表明向土壤中输入不稳定的 C 可以促进物理化学保护的 SOM 的形成，这可能涉及转化为微生物残留物以及随后与金属阳离子和/或矿物质的相互作用，也可能由土壤性质介导. 受保护的 SOM 的形成可能会抵消原生 SOM 的分解，因此对长期陆地碳储存具有重要的生态意义。